JP2001071117A - Cylinder block casting method and its cast product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the partial deformation of a preform in a cavity caused by the pouring pressure of molten metal without separately using a large-scaled suction apparatus or the like. SOLUTION: The cylindrical preform having a prescribed vol. ratio is fitted onto the outer periphery of a bore pin by being entagled with wear resistant metallic fibers. The molten metal is supplied into the cavity from molten metal supplying passages set in the forming positions of journal parts 3a-3e to constitute the inner peripheral surface portions of a cylinder bores with the preforms. In this way, the state the partial diameter-expansion deformation near the journal parts 3a-3e is caused in the preforms is prevented with a rigid member 21 fitted to the bore pin. The molten metal is allowed to be easily infiltrated by reducing the vol. ratio (enlarging porosity) only at the portion nearer to the molten metal supplying portion in the preform, thus the above mentioned deformation can be prevented. The preform is pressurized in the compressing direction with the molten mold pressure by slitting the molten metal supplying position so as to be positioned at the outer periphery of the preform, thus the above mentioned deformation can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder block casting method and a cast product thereof.

[0002]

2. Description of the Related Art In an engine, for example, an automobile engine, a cylinder block is often formed of a light metal such as an aluminum alloy in order to reduce the weight. On the other hand, the functions required for specific parts of the cylinder block,
For example, in some cases, the metal constituting the cylinder block may not be sufficiently satisfactory to secure sufficient wear resistance of the inner surface of the cylinder bore. For this reason, it is common practice to separately fit a cylinder liner into the cylinder bore, but in addition, a porous metal called a preform is also cast during cylinder block casting (Japanese Unexamined Patent Publication No.
-14045). For example, in order to secure the wear resistance of the inner surface of the cylinder bore, a cylindrical preform having a predetermined volume ratio is fitted around the outer periphery of a bore pin serving as a cylinder bore forming core, and the preform is cast. Has been done.

[0003] Since the preform is usually formed so as to be porous by entanglement of metal fibers, the molten metal sufficiently penetrates into the voids and is firmly integrated with the cylinder block. On the other hand, it is preferable in terms of point, but since the rigidity is small as a whole, partial deformation (positional displacement) is likely to occur when a large pressure is applied during injection of the molten metal. Japanese Patent Application Laid-Open No. 6-106329 proposes pouring while sucking a preform in order to prevent deformation of a preform in a mold, that is, in a cavity.

[0004]

The deformation of the preform at the time of pouring will be specifically described. For example, when the abrasion resistance of the inner surface of the cylinder bore is ensured by the preform, the cylindrical preform is formed around the outer periphery of the bore pin. In this state, the molten metal is usually injected from the part forming the journal portion of the cylinder block, that is, from the direction toward the piston bottom dead center to the direction toward the piston top dead center. Become. In this case, the pressure of the molten metal acts on the preform from the direction of the piston bottom dead center, but due to the formation of the jar,
The pressure of the molten metal acts on only a part of the cylindrical preform in the circumferential direction. As a result, the preform is separated from the bore pin from the certain portion, that is, the preform is partially deformed in a radially outward direction. In order to prevent such expansion deformation,
For example, on a part of a mold defining a cavity, a shelf for preventing the molten metal from acting on the certain part (a projection having a lid function for restricting the flow of the molten metal) or a shelf for restricting the diameter of the preform ( It is conceivable to form the projections), but in this case, the shelf becomes a hindrance, making it impossible to remove the mold, and cannot be adopted.

On the other hand, Japanese Patent Application Laid-Open No.
As proposed in Japanese Patent Publication No. 29, performing a separate suction to prevent the preform from being deformed at the time of pouring requires a large-scale suction device, which is not preferable.

Accordingly, an object of the present invention is to prevent a preform set in a cavity from being deformed at the time of pouring without separately using a large-scale device such as a suction device. An object of the present invention is to provide a method of casting a cylinder block and a cast product thereof.

[0007]

Means for Solving the Problems To achieve the above object, a method for casting a cylinder block according to the present invention is as follows as a first solution. That is, as described in claim 1 of the claims,
A cylinder block casting method of setting a cylindrical preform having a predetermined volume ratio in a cavity in a mold, injecting a molten metal into the cavity, and casting a cylinder block in which the preform is cast. In the preform, a specific portion corresponding to the side into which the molten metal is injected has a higher rigidity than other portions. Preferred embodiments based on the above solution are as described in claims 2, 3 and 7 in the claims.

In order to achieve the above object, a method for casting a cylinder block according to the present invention is as follows as a second solution. That is, as described in claim 4 of the claims, a cylindrical preform having a predetermined volume ratio is set in a cavity in a mold,
In the casting method of a cylinder block, in which a molten metal is injected into the cavity and the preform is cast into a cylinder block, the preform is fitted around a bore pin serving as a cylinder bore forming core. A cylindrical rigid member, which is disposed in the cavity in a state and through which the molten metal can pass, is fitted around the outer periphery of the preform, and the rigid member moves the preform radially outward of the bore pin. The molten metal is injected into the cavity in a state where the rigid member is fitted to the outer periphery of the preform, and the rigid member is cast around with the preform. is there. A preferable mode based on the above solution is as described in claim 7 of the claims. A method for casting a cylinder block.

In order to achieve the above object, a third method of casting a cylinder block according to the present invention is as follows. That is, as described in claim 5 of the claims, a cylindrical preform having a predetermined volume ratio is set in a cavity in a mold,
In a cylinder block casting method for casting a molten metal into the cavity to cast a cylinder block in which the preform is filled, a volume ratio of a specific portion of the preform corresponding to a side into which the molten metal is injected. Is made smaller than the volume ratio of the other parts.
Preferred embodiments based on the above solution are as described in claims 6 and 7 in the claims. A method for casting a cylinder block.

In order to achieve the above object, a method for casting a cylinder block according to the present invention is as follows as a fourth solution. That is, as described in claim 8 in the claims, a cylindrical preform having a predetermined volume ratio is set in a cavity in a mold,
Injecting molten metal into the cavity, a method of casting a cylinder block in which the preform is cast into a cylinder block, wherein the molten metal is injected from a direction in which the preform is compressed radially inward. It is like that.

The first one of the cylinder block, that is, the cast product in the present invention is as follows. That is, in a cylinder block in which a cylindrical preform having a predetermined volume ratio is cast in an inner peripheral surface portion of a cylinder bore, as described in claim 9 in the claims, of the preform, The rigidity of the specific portion on the side of the dead center is set to be greater than the rigidity of the other portions. A preferable mode based on the above solution is as described in claim 10 of the claims.

The second one of the cylinder block, that is, the cast product in the present invention is as follows. That is, as described in claim 11 in the claims, in a cylinder block in which a cylindrical preform having a predetermined volume ratio is cast in an inner peripheral surface portion of a cylinder bore, the cylindrical rigid member has the cylindrical rigid member, It is inserted with the preform in a state fitted to the outer periphery of the preform.

The third one of the cylinder block, that is, the cast product in the present invention is as follows. That is, in a cylinder block in which a cylindrical preform having a predetermined volume ratio is cast in an inner peripheral surface portion of a cylinder bore as described in claim 12 of the claims, the preform includes a piston lower portion. The volume ratio of the specific portion on the dead center side is smaller than the volume ratio of the other portion.

The fourth cylinder block, that is, the cast product of the present invention is as follows. That is, as set forth in claim 13, in a cylinder block in which a cylindrical preform having a predetermined volume ratio is filled in an inner peripheral surface portion of a cylinder bore, a molten metal for casting a cylinder block. The injection position includes a position in a direction of compressing the preform radially inward.

[0015]

According to the first aspect of the present invention, since the rigidity of the specific portion of the preform on the side to be poured is increased, deformation of the preform at the time of pouring can be prevented or reduced. This is preferable in that the reform is properly cast into the predetermined position of the cylinder block. It is to be noted that increasing the rigidity of the preform as a whole is not preferable because the volume ratio is largely different from the predetermined volume ratio as a whole. According to the second aspect, the rigidity of the specific portion can be easily and surely increased by using the rigid member which is a member separate from the preform. According to the third aspect, in the vicinity of the end of the bore pin, the preform is easily deformed in the diameter-expanding direction due to the molten metal entering from between the bore pin and the preform. The flow of the molten metal can be regulated.

According to the fourth aspect, it is possible to reliably prevent the preform from expanding in diameter by using the cylindrical rigid member. According to the fifth aspect, the preform is configured to allow the molten metal to easily penetrate into a specific portion near the pouring position of the preform, that is, to release the pressure of the molten metal for expanding the diameter of the preform. Can be prevented from being deformed. According to the sixth aspect, a difference in volume ratio can be obtained by a technique of changing the thickness of the preform. According to the seventh aspect, the injection position of the molten metal into the cavity can be set from the side where the general journal portion is formed. According to claim 8, the diameter expansion deformation of the preform can be prevented only by devising the injection direction of the molten metal. According to claim 9, a cylinder block obtained by the casting method according to claim 1 is provided. According to claim 10, there is provided a cylinder block obtained by the casting method according to claim 2. According to claim 11, a cylinder block obtained by the casting method according to claim 4 is provided. According to claim 12, a cylinder block obtained by the casting method according to claim 5 is provided. According to claim 13,
A cylinder block obtained by a casting method according to claim 8 is provided.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1 and 2, reference numeral 1 denotes a cylinder block in an automobile engine, which is cast from an aluminum alloy. This cylinder block 1 is for a V-type 6 cylinder, and 2a to 2f are cylinder bores into which pistons are slidably fitted.
Numeral 3e is a journal portion serving as a bearing portion of the crankshaft. The preform 4 is cast in the inner surface of each of the cylinder bores 2a to 2f at the time of casting the cylinder block, and the preform 4 ensures sufficient wear resistance of the inner surfaces of the cylinder bores 2a to 2f.

The preform 4 has a porous structure in which internal voids are communicated with each other like open cells by entanglement of metal fibers having wear resistance. The preform 4 has a predetermined volume ratio (the ratio of the metal fibers to the entire volume of the preform 4; the larger the volume ratio, the larger the ratio of the metal fibers) from the viewpoint of ensuring the wear resistance of the inner surface of the cylinder bore. (For example, 30%), and is cast when the cylinder block 1 is cast in a state of being formed into a cylindrical shape in advance. Note that a preform having a predetermined volume ratio is commercially available as a sheet, and the sheet is formed into a cylindrical shape, and is used for casting into the cylinder block 1.

FIG. 3 shows a first embodiment of the present invention and shows an example of a mold for casting a cylinder block.
In FIG. 3, reference numeral 11 denotes an upper die, 12 denotes a lower die, 13 denotes a bore pin serving as a core for forming a cylinder bore, and the bore pin 13 is detachably fixed to the upper die 11. Bore pin 1
A cylindrical preform 4 having a predetermined volume ratio is fitted around the outer periphery of the cylinder 3 without play. In FIG. 3, the lower part of the bore pin 13 is on the piston bottom dead center side,
Is located at the top dead center side of the piston. The molten metal is supplied from the bottom dead center side of the piston, that is, from the side forming the journal portions 3a to 3f. That is, from one common molten metal supply path (not shown), a plurality of branch supply paths 14a, 14b,.
In the cylinder block 1 shown in FIG. 1, the molten metal is directed upward from a portion forming the front wall portion 1a, each of the journal portions 3a to 3e, and the rear wall portion 1b of the cylinder block 1. It is supplied (only the branch supply paths 14a and 14b are shown in FIG. 3). Of the cavities 15 in the mold, 15a is for forming the first journal portion 3a, 15b is for forming the front wall portion 1a,
15c is for forming a second journal portion, and 15d is for forming a partition wall between adjacent cylinder bores.

A member having excellent rigidity, for example, a rigid member 16 made of the same metal (eg, aluminum alloy) as the metal to be melted to form the cylinder block 1 is attached to a lower portion of the bore pin 13. This rigid member 1
6 is a ring-shaped, that is, a short cylindrical shape, which is fitted to the lower portion of the bore pin 13 without play and is seated on the lower mold 12 and the outer peripheral edge of the main body 16a. And a locking projection 16b that rises shortly upward. The lower end surface of the preform 4 is seated on the main body 16a,
Supported. The locking projection 16b is fitted around the lower end of the preform 4 without play. As a result, the lower end of the preform 4 is restricted from being deformed in the radially expanding direction by the locking projection 16b, and the bore pin 1
3 is maintained in a state of being in close contact. Also, the preform 4 fitted to the bore pin 13
Although a part of its circumferential direction faces (exposes) the branch supply path 14b when the rigid member 16 is not present,
Due to the main body 16a of the rigid member 16, this branch supply 1
The portion facing 4b will be covered. That is, the contact position between the preform 4 and the bore pin 13 (the bore pin 13
Between the outer peripheral surface and the inner peripheral surface of the preform 4).
As a result, the lid is covered from below, and the intrusion of the molten metal from below into this contact position is regulated.

In the setting completion state shown in FIG. 3, the molten metal is supplied into the cavity 15 from the branch supply paths 14a, 14b and the like. Depending on the supplied molten metal, the cylinder block 1
Is cast, and at this time, the preform 4 and the rigid member 16 are respectively cast. After the molten metal solidifies, the mold is opened to obtain a cylinder block 1 as shown in FIGS.

When the molten metal is supplied into the cavity 15, since the rigid member 16 is not present in the related art, the molten metal from the branch supply path 14 b flows between the lower end of the bore pin 13 and the lower end of the preform 4. The preform 4 attempts to partially expand radially outwardly in the radial direction, and such intrusion of the molten metal is restricted by the main body 16 a of the rigid member 16. The deformation of the preform 4 toward the radially outward side is restricted by the locking projection 16b of the member 16. As a result, the preform 4 is cast into the cylinder block 1 in a state where it is properly positioned at the desired position.

FIG. 4 shows a second embodiment of the present invention. In the present embodiment, another type of rigid member 21 is used in place of the rigid member 16 of FIG. The rigid member 21 has a substantially flat ring shape as a whole, and differs from the rigid member 16 in FIG. 3 in that the rigid member 21 does not have the locking projection 16b. The lower end of the bore pin 13 is partially formed as a small diameter portion 13a, and the rigid member 21 is fitted to the small diameter portion 13a without play. This rigid member 21 is also cast together with the preform 4. The rigid member 21 includes the bore pin 13 and the preform 4
It acts to restrict the infiltration of the molten metal from below with respect to the contact position. That is, the rigid member 21 functions as the main body 16a of the rigid member 16 in FIG. In addition, the rigid member 21 is restricted from being displaced upward with respect to the bore pin 13 by the locking step 13b formed between the rigid member 21 and the large diameter portion formed by forming the small diameter portion 13a. (Even under the pressure of the molten metal from below,
The rigid member 21 is reliably positioned at the predetermined set position in FIG. 4 without being displaced upward, and restricts the upward pressing force from acting on the preform 4).

FIG. 5 shows a third embodiment of the present invention. In the present embodiment, the outer periphery of the preform 4 is almost entirely covered with a long cylindrical rigid member 31 having excellent rigidity. Although the rigid member 31 is fitted to the outer periphery of the preform 4 without play, the molten metal is allowed to pass through so that the molten metal can enter the preform 4 from the periphery. The rigid member 31 through which the molten metal can pass can be formed of, for example, an aluminum alloy punched metal. In the present embodiment, the rigid member 31 reliably prevents the preform 4 from expanding in diameter. In order to more reliably position the rigid member 31, at least one of the upper end and the lower end thereof may be fitted in an annular locking groove formed in the upper mold 11 or the lower mold 12. Note that the rigid member 31 may be short and fitted to only the lower end of the preform 4 (the function of the locking projection 16b in FIG. 3 is performed).

FIGS. 6 to 10 show a fourth embodiment of the present invention. As the preform 4, the volume ratio of a portion at the bottom dead center side of the piston, which is easily expanded and deformed, that is, a specific portion, is shown. A volume ratio smaller than that of the portion is used. Thus, the metal occupation ratio of the specific portion is small (the void ratio of the specific portion is large), and the molten metal easily penetrates into the specific portion, thereby preventing the specific portion from expanding and deforming. It is like that. That is, it is difficult to reduce the volume ratio of the part other than the specific part, particularly the upper part of the cylinder bore 4 on which the piston pin slides, from the viewpoint of abrasion resistance to the extent that the expansion deformation can be prevented. Since the piston pin is not slid in the specific portion, there is no particular problem even if the volume ratio is reduced.

An example for obtaining the preform 4 having a partially different volume ratio as described above will be described. First, as shown in FIG. 6, a cylindrical outer preform 4B having a uniform volume ratio is fitted around the outer periphery of a cylindrical inner preform 4A having a uniform volume ratio. . Thereafter, an external force is applied to form the inner / outer double preform 4 so that the radial dimension, that is, the thickness, gradually changes in the longitudinal direction as shown in FIG. In the embodiment, the volume ratio at the upper end in FIG.
The volume ratio at the lower end is, for example, 6%, and the volume ratio gradually increases from the lower end to the upper end.

In order to mold the preform 4 as shown in FIG. 7, for example, a mold as shown in FIG. 10 is used. That is, in FIG. 10, reference numeral 41 denotes an upper mold, 42 denotes a lower mold, and 43 denotes a plurality of divided lateral molds each of which has an arc shape and cooperates with each other when closed. On the mold 42, a projection 42a gradually tapering is formed. The preform 4 shown in FIG.
At this time, the preform 4 is fitted with a large gap to the small-diameter distal end portion of the projection 42a. By closing the side mold 43 in this state, a preform 4 as shown in FIG. 7 is obtained.

The preform 4 of FIG. 7 is set in a mold such that the side with the larger volume ratio is on the top dead center side of the piston (the side with the smaller volume ratio is on the bottom dead center side of the piston). Thereafter, the molten metal is supplied.
Since the volume ratio is small, the molten metal easily penetrates into the portion having the small volume ratio, so that this portion (the piston bottom dead center side portion) is prevented from being deformed radially outward.
The cast cylinder block 1 is obtained as shown in FIG. Cylinder block 1 immediately after being removed from the mold
Since the inner diameter of the cylinder bore is larger at the piston top dead center side than at the bottom dead center side, if necessary, the inner diameter at the piston bottom dead center side is the same as the inner diameter at the top dead center side,
Machine processing such as grinding may be performed.

FIGS. 11 and 12 show a fifth embodiment of the present invention, and show another method for obtaining a preform 4 having a different volume ratio in the longitudinal direction. That is, first, as shown in FIG. 11, an outer preform 4D having an overall uniform volume ratio is fitted only to an upper portion of the outer periphery of a cylindrical inner preform 4C having an overall uniform volume ratio. The combined is formed. After this,
By compressing only the inner and outer double portions of FIG. 11, a preform 4 having a uniform inner and outer shape as a whole but having a larger volume ratio of only the upper portion is obtained as shown in FIG. The cylinder block is cast by setting the inner and outer double structure portions having a large volume ratio in the mold so as to be located on the top dead center side of the piston. The inner preform 4C has a small volume ratio so that the molten metal easily penetrates (the volume ratio is smaller than a volume ratio at which sufficient wear resistance is obtained).

FIG. 13 shows a sixth embodiment of the present invention, in which the position of the molten metal supply to the cavity 15 is devised to prevent the preform 4 from expanding and deforming. That is, the branch supply path 14b is abolished, and the supply path 14x corresponding to the branch supply path 14b is replaced with the cavity 1 on the side of the preform 4 where the diameter is easily deformed.
5 (the supply path 14x extends from the lower mold 12 to the upper mold 11). As a result, (the pressure of) the molten metal supplied from the supply path 14x acts on (the lower end of) the preform 4 from the radially outward side, and the preform 4 is deformed radially outwardly. Is prevented.

Although the embodiment has been described above, the preform 4 is not limited to the case where the preform 4 is used for forming the inner surface portion of the cylinder bore. It can be used at an appropriate position such as for forming an inner surface portion. The purpose of the present invention is not limited to what is explicitly specified, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

[Brief description of the drawings]

FIG. 1 shows an example of a cylinder block to which the present invention is applied, and is a bottom view as viewed from a journal portion side.

FIG. 2 is a sectional view of a main part showing a state of a cylinder bore portion of a cylinder block formed according to the present invention.

FIG. 3 is an essential part cross-sectional view showing a state where a preform is set in a mold together with a rigid member.

FIG. 4 is an essential part cross-sectional view showing a state where a preform is set in a mold together with another rigid member.

FIG. 5 is an essential part cross-sectional view showing a state where a preform is set in a mold together with another rigid member.

FIG. 6 is a cross-sectional view showing a preparation step when forming a preform having a partially different volume ratio.

FIG. 7 is a cross-sectional view showing the preform in a state where the volume ratio is partially different from the preparatory process of FIG. 6;

FIG. 8 is a sectional view of a main part showing a state where the preform shown in FIG. 7 is set in a mold.

FIG. 9 is a sectional view of a main part of the cylinder block obtained from the state of FIG. 8;

FIG. 10 is a sectional view showing an example of a molding die used to obtain the preform in the state of FIG. 6 from the state of FIG. 6;

FIG. 11 is a cross-sectional view showing another example of a preparation step in the case of forming a preform having a partially different volume ratio.

FIG. 12 is a cross-sectional view showing a preform in a state where the volume ratio is partially different from the preparatory process of FIG. 11;

FIG. 13 is an essential part cross-sectional view showing an example of a case where a molten metal supply position into a cavity is set as a specific position.

[Explanation of symbols]

 1: Cylinder block 2a to 2f: Cylinder bore 3a to 3e: Journal part 4: Preform 11: Upper die 12: Lower die 13: Bore pin 14a, 14b: Branch molten metal supply path 15: Cavity 16, 21, 31: Rigid member 14x : Branch molten metal supply path (specific position)

Continued on the front page (72) Inventor Yukihiro Sugimoto 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda F-term (reference) 3G024 AA25 AA26 BA02 DA19 EA01 FA01 FA06 GA02 GA10 GA36 HA07 HA18

Claims (13)

[Claims] 1. A cylinder block for setting a cylindrical preform having a predetermined volume ratio in a cavity in a mold, injecting molten metal into the cavity, and casting a cylinder block in which the preform is filled. The casting method according to any one of claims 1 to 3, wherein, in the preform, a specific portion corresponding to a side into which the molten metal is injected has a higher rigidity than other portions. 2. The cylinder according to claim 1, wherein the rigidity of the specific portion is ensured by a rigid member that is formed of a member separate from the preform and that is cast together with the preform. Block casting method. 3. The preform according to claim 2, wherein the preform is disposed in the cavity while being fitted to an outer periphery of a bore pin serving as a core for forming a cylinder bore. Disposed in the cavity so as to cover a contact portion with the
A method for casting a cylinder block. 4. A cylinder block for setting a cylindrical preform having a predetermined volume ratio in a cavity in a mold, injecting a molten metal into the cavity, and casting a cylinder block in which the preform is cast. In the casting method of (1), the preform is disposed in the cavity while being fitted to an outer periphery of a bore pin serving as a core for forming a cylinder bore, and a cylinder through which molten metal can pass through the outer periphery of the preform. The rigid member is fitted, and the rigid member restricts the preform from spreading radially outward of the bore pin. The rigid member is fitted around the outer periphery of the preform. A method for casting a cylinder block, wherein a molten metal is injected into a cavity and the rigid member is cast together with the preform. 5. A cylinder block for setting a cylindrical preform having a predetermined volume ratio in a cavity in a mold, injecting a molten metal into the cavity, and casting a cylinder block in which the preform is filled. The casting method according to any one of claims 1 to 3, wherein, in the preform, a volume ratio of a specific portion corresponding to a side where the molten metal is injected is made smaller than a volume ratio of another portion. Method. 6. The method for casting a cylinder block according to claim 5, wherein the thickness of the specific portion is larger than the thickness of the other portion. 7. The cylinder block casting according to claim 1, wherein the injection of the molten metal is performed from at least a portion of the cavity where a journal is formed. Method. 8. A cylinder block for setting a cylindrical preform having a predetermined volume ratio in a cavity in a mold, injecting a molten metal into the cavity, and casting a cylinder block in which the preform is filled. The casting method according to any one of claims 1 to 3, wherein the molten metal is injected from a direction in which the preform is compressed radially inward. 9. A cylinder block in which a cylindrical preform having a predetermined volume ratio is cast in an inner peripheral surface portion of a cylinder bore, wherein a specific portion of the preform closer to a piston bottom dead center has a different rigidity. Is greater than the rigidity of the part,
A cylinder block characterized by the above-mentioned. 10. The cylinder according to claim 9, wherein the rigidity of the specific portion is secured by a rigid member formed of a member separate from the preform and cast together with the preform. block. 11. A cylinder block in which a cylindrical preform having a predetermined volume ratio is cast in an inner peripheral surface portion of a cylinder bore, wherein a cylindrical rigid member is fitted to an outer periphery of the preform. A cylinder block, which is cast together with the preform. 12. A cylinder block in which a cylindrical preform having a predetermined volume ratio is cast in an inner peripheral surface portion of a cylinder bore. A volume ratio of the cylinder block is smaller than that of another portion. 13. In a cylinder block in which a cylindrical preform having a predetermined volume ratio is cast in an inner peripheral surface portion of a cylinder bore, a molten metal injection position compresses the preform radially inward. A cylinder block that is set to be in a direction.